Methods and apparatus for testing earth formations

ABSTRACT

In the representative embodiments of the new and improved methods and apparatus for testing earth formations disclosed herein, fluid-admitting means are placed into sealing engagement with a potentially-producible earth formation and selectivelyoperable valve means on the fluid-admitting means are opened to place a filtering medium situated between the fluid-admitting means and a flow line in communication with the isolated formation. Then, before testing is commenced, well bore fluids are introduced into the flow line and discharged through the filtering medium in a reverse direction and into the earth formation for cleaning the filtering medium of potentiallyplugging materials before connate fluids are introduced into the fluid-admitting means.

Urbanosk et a .Bnne d, WM

[ METHODS AND APPARATUS FOR TESTiNG 3,577,731 5/1971 Lebourg 73/1523,653,436 4/1972 Whitten l66/l00 EARTH FORMATHONS William R. Sherman;Stewart F. Moore in the representative embodiments of the new andimproved methods and apparatus for testing earth formations disclosedherein, fluid-admitting means are placed into sealing engagement with apotentiallyproducible earth formation and selectively-operable valvemeans on the fluid-admitting means are opened to place ,a filteringmedium situated between the fluidadmitting mfins and a flow line incommunication with the isolated formation. Then, before testing iscommenced, well bore fluids are introduced into the flow line anddischarged through the filtering medium in a reverse direction and intothe earth formation for cleaning the filtering medium ofpotentially-plugging materials before connate fluids are introduced intothe fluid-admitting means.

[75] Inventors: Harold J. Urhanoslty, Pearland;

Frank R. Whitten, Houston, both of Tex.

[73] Assignee: Schlumberger Technolog Corporation, New York, NY. [22-]Filed: Dec. 8, 1972 [2]] Appl. No.: 313,225

[52] U8. Cl. 73/l55, 73/421 R [51] Int. Cl EZlh dQ/tlh [58] Field ofSearch 73/155, 421 R, 151, 152; '166/100 [56] References Cited UNITEDSTATES PATENTS 3,0] l,554 l2/l 96l Desbrandes et al. l66/l00 3.254.5316/1966 Briggs..lr..... 3.352,36l ll/l967. Urbanosky 3,530,933 9/l97()Whitten l66/lOO' 3.565,l69 2/l97l Bell l66/l00 PAEENEEM an POWER SUPPLYi METHODS AND ArrAnATus son "merino even should it be quickly realizedthat a particular sampling or testing operation already underway willprobably be unsuccessful, the operator has no choice except todiscontinue the operation and then return the tool to the surface. Thisobviously results in a needless loss of time and expense which wouldusually be avoided if another attempt could be made without having toremove the tool from the well bore.

One of the most significant problems which have heretofore prevented theproduction of a commercially successful repetitively-operableformation-testing tool has been in providing a suitable arrangement forreliably establishing fluid or pressure communication with imcompetentor unconsolidated earth formations. Although the several new andimproved testing tools respectively shown in U.S. Pat. No. 3,352,361,U.S. Pat, No. 3,530,933, U.S. Pat. No. 3,565,169 and U.S. Pat. No.3,653,436 are especially arranged for testing unconsolidated formations,for one reason or another these tools are not adapted for performingmore than one testing operation during a single run in a given wellbore. For example, as described in these patents, each of these new andimproved testing tools employs a tubular sampling member which iscooperatively associated with a filtering medium for preventing theunwanted entrance of unconsolidated formation materials into the testingtool. Experience has shown, however, that although these new andimproved filtering arrangements are highly successful for a singleoperation, subsequent tests cannot be reliably performed since particlesof mudcake and exceptionally-fine formation materials will often coat orplug the filtering medium.

Thus, following each test, the testing tool must be reattained in thepractice of the new and improved methods described herein by placingnormally-closed fluidadmitting means having filtering meanscooperatively arranged therewith into sealing engagement with an earthformation, opening communication between the filtering means and theearth formation, and discharging well bore fluids in a reverse directionthrough the filtering medium and into the formation for cleansing thefiltering medium of unwanted possibly-plung matter such as mudcake andloose formation materials.

To further achieve the obiects of the prwent invention, formationtestingapparatus is provided with fiuidadmitting means pted to be seaiingiyengaged with a potentialiyproducible earth formation. To limit theentrance of loose formation materials into the fluidadmitting means,filtering means are disposed in the fluid-admitting means.Normaliy-closed valve means are cooperatively arranged in thefluid-admitting means for seiective movement to an open position foropening communication between an isolated earth formation and thefiltering means. Means are further provided for discharging well borefluids in i3 reverse direction through the filtering means upon openingof the valve means for flushing possibly-plugging materials away fromthe filtering means.

The novel features of the present invention are set forth withparticularity in the appended claims. The invention, together withfurther objects and advantages thereof, may be best understood by way ofthe following description of exemplary apparatus employing theprinciples of the invention as illustrated in the accompanying drawings,in which:

H0. 1 depicts the surface and downhole portions of a preferredembodiment of new and improved formadon-testing apparatus for practicingthe invention and incorporating its principles;

FiGS. 2A and 28 together show a somewhatschematic representation of theformation-testing tool illustrated in FIG. 1 as the tool will appear inits initiai operating position; and v FIGS. 3-5 A and Brespe'ctively'depict the successive positions of various componentsjofthe new and improved tool shown in FIGS. 2A and 28 during the course ofa typical testing and sampling operation. Turning now to FIG. i, apreferred embodiment of a new and improved sampling and measuring too!it? incorporating the principles of the present invention is shown as itwill appear during the course of a typical measuring and samplingoperation in a well bore such as a borehole i1 penetrating one or moreearth formations as at 12 and 13. As illustrated, the tool id issuspended in the borehole it from the lower end of a typi calmulticonductor cable 14 that is spooied in the usual fashion on asuitable winch (not shown) at the surface and coupled to the surfaceportion of a tool-control system 15 as well as typical recording andindicating apparatus l6 and a power supply 117. in its preferredembodiment, the tool 10 includes anelongated body 18 which encloses thedownhole portion of the tool control system 15 and carriesselectively-extendibie toolanchoring means i9 and new and improvedfluidadmitting means 20 arranged on opposite sides. of the body as wellas one or more tandemly-coupled fluid collecting chambersZi and 22.

As is explained in greater detail in a copending appiication, Ser. No.313,235 by Harold J. Urbanosityfiied Dec. 8, 1972, the new and improvedformation-testing tool 10 of the present invention and the controlsystem 35 are cooperatively arranged so that, upon command from thesurface, the tool can be selectively placed in any one or more of fiveselected operating positions. As will be subsequently described briefly,the control system 15 will function to either successively piece thetool in one or more of these positions or else cycle the tool betweenselected ones of these operating positions. These five operatingpositions are simply achieved by selectively moving suitable controlapply power to different conductors Fill-3'7 in the cable Turning now toFlGS. 2A and 2B, the preferred embodiment of the entire downhole portionof the control system 15 as well as the tool-anchoring means 19, the

fluid-admitting means 263 and the fluid-collecting chambers 21 and 22are schematically illustrated with their several elements or componentsdepicted as they will respectively be arranged when the new and improvedtool is fully retracted and the switches 23 and 24 are in their first oroff operating positions 25. In the preferred embodiment of theselectivelyextendible tool-anchoring means l9 schematically illustratedin FIG. 2A, an upright wall-engaging anchor member 38 along the rear ofthe tool body lid is coupled in a typical fashion to alongitudinallyspaced pair of laterally-movable piston actuators 39 and dll of a typical design mounted tranversely on the tool body lif As willbe subsequently explained, the lateral extension and retraction of thewall-engaging member 3% in relation to the rear of the tool body ibiscontrolled by the control system which is operatively arranged to se'lectively admit and discharge a pressured hydraulic fluid to and fromthe piston actuators 39 and 4t).

borehole fluid-admitting means it) employed with the preferredembodiment of the new and improved tool 10 are cooperatively arrangedfor sealingoff or isolating selected portions of the wall of thehorehole 11; and, once a selected portion of the borehole wall ispacked-off or isolated from the well bore fluids, establishing pressureor fluid communication with the adjacent earth-formations. As depictedin H6. 2A, the fluid-admitting means preferably include an annularelastomeric sealing pad 41 mounted on the forward face of an uprightsupport member or plate 42 that is coupled to a longitudinally-spacedpair of laterallymovable piston actuators 43 and 44 respectivelyarranged transversely on the tool body 18 for moving the sealing pad inrelation to the forward side of the tool body. Accordingly, as thecontrol system l5 selectively supplies a pressured hydraulic fluid tothe piston actuators 43 and 44, the sealing pad 41 will be movedlaterally between a retracted position adjacent to the forward side ofthe tool body 18 and an advanced or forwardly-extended position.

By arranging the annular sealing member 41 on the opposite side of thetool body l8 from the wallengaging member 38, the lateral extension ofthese two members will, of course, be effective for urging the sealingpad into sealing engagement with the adjacent wall of the borehole 11and anchoring the tool It) each time the piston actuators 39, 40, 43 and44 are extended. It will, however, be appreciated that the wallengagingmember 38 as well as its piston actuators 39 and 40 would not be neededif the effective stroke of the piston actuators 43 and 44 would besufiicient for assuring that the sealing member 4ll can be extended intofirm sealing engagement with one wall of the borehole 11 with the rearof the tool body l8 securely anchored against the opposite wall of theborehole. Conversely, the piston actuators 43 and 44 could be similarlyomitted where the extension of the wall-engaging member 38 alone wouldbe effective for moving the other side of the tool body 18 forwardlytoward one wall of the borehole it to place the sealing pad @l into firmsealing engagement therewith. However, in the preferred embodiment ofthe formation-testing tool 10, both the tool-anchoring means 19 and thefluidadrnitting means 2ft are made selectively ertendible to enable thetool to be operated in boreholes of substantial diameter. This preferreddesign of the tool it'll, of course, results in the overall strolre ofthe piston actuators 39 and an and the piston actuators did and dd beingto a minimum so as to reduce the overall diameter of the tool body lb.

To conduct connate fluids into the new and improved tool l@, thefluid-admitting means 2t? further include an enlarged tubular member d5having an open ion ward portion coaxially disposed within the sealingpad er and a closed rear portion which is slidably mounted within alarger tubular member secured to the rear face of the plate 42 andextended rearwardly there'- from. By arranging the nose of the tublarfluid admitting member 4% to normally protrude a short distance ahead ofthe forward face of the sealing pad til, extension of thefluid-admitting means 20 will engage the forward end of the fluidadrnitting member with the adjacent surface of the wall of the boreholell as the annular sealing pad is also forced thereagainst for isolatingthat portion of the borehole wall as well as the nose of the fluidadrnitting member from the well bore fluids. To selectively movethetubular fluid-admitting member 45 in relation to the enlarged outermember as, the smaller tubular member is slidably disposed within theouter tubular member and fluidly, sealed in relation thereto as'bysealing members 47 and db on in wardly-enlarged end portions 439 and 55dof the outer member and a sealing member ll on an enlargeddiameterintermediate portion 2 of the inner member.

Accordingly, it will be appreciated that by virtue of the sealingmembers 47', id and 5t, enclosed piston chambers 53 and 5d are definedwithin theouter tubular member did and on opposite sides of theoutwardlyenlarged portion 52 of the inner tubular member 35 which, ofcourse, functions as a piston member. Thus, by increasing the hydraulicpressure in the rearward chamber $3, the fluid-admitting member 45 willbe moved forwardly in relation to the outer tubular member 46 as well asto the sealing pad dll. Qonversely, upon the application of an increasedhydraulic pressure to the forward piston chamber 54, the fluid-admittingmember 45 will be retracted in'relation to the'outer member 46 and thesealing pad ill.

Pressure or fluid communication with the fluidadmitting menas 2b iscontrolled by means such as a generally-cylindrical valve member 55which is coard-v ally disposed within the fluid-admitting member Q5 andcooperatively arranged for axial movement therein be tween a retractedor open position and the illustrated advanced or closed position wherethe enlarged forward end 56 of the valve member is substantially, if notaltogether, sealingly engaged with the forwardmost interior portion ofthe fluid-admitting member. To support the valve member 55, the rearwardportion of the valve member is axially hollowed, as at d7, and coaxiallydisposed over a tubular member 5h projecting for" wardly from thetransverse wall 59 closing the rear end of the fluid-admitting member4l. The axial bore 5'7 is reduced and extended forwardly along the valvemember 55 to a termination with one or more transverse fluid passages inthe forward portion of the valve member just behind its enlarged headas.

To provide piston means for selectively moving the valve member 55 inrelation to the fluid-admitting member 45, the rearward portion of thevalve member is enlarged, as at 61, and outer and inner sealing members62 and 63 are coaxially disposed thereon and respectively sealinglyengaged with the interior of the fluid-admitting member and the exteriorof the forwardly-extending tubular member A sealing member 64 mountedaround the intermediate portion of the valve member 55 and sealinglyengaged with the interior wall of the adjacent portion of thefluid-admitting member 45 fluidly seals the valve member in relation .tothe fluid-admitting member. Accordingly, it will be Those skilled in theart will, of course, appreciate that many earth formations, as at l2,are relatively unconsolidated and are, therefore, readily eroded by thewithdrawal of connate fluids. Thus, to prevent any significant erosionof such unconsolidated formation materials, the fluid-admitting member45 is arranged to define an internal annular space 67 and allow passage68 in the forward portion of the fluid-admitting member, and a tubularscreen 69 of suitable fineness is coaxially mounted around the annularspace. in this manner, when the valve member 55 is retracted, formationfluids will be compelled to pass through the exposed forward portion ofthe screen 69 ahead of the enlarged head 56, into the annular space 67,and then through the fluid passage 60 into the fluid passage 57 and thetubular member 58. Thus, as the valvemember 55 is retracted, shouldloose or unconsolidated formation materials be eroded from a formationas connate fluids are withdrawn therefrom, the materials will be stoppedby the exposed portion of the screen 69 ahead of the enlarged head 56 ofthe valve member thereby quickly forming a permeable barrier to preventthe continued erosion of loose formation materials once the valve memberhalts.

A sample or flow line 70 is cooperatively arranged in theformation-testing tool and has one end coupled, as by a-flexible conduit71, to the fluid-admitting means and its other end terminated in a pairof branch conduits 72 and 73 respectively coupled to the fluidcollectingchambers 21 and 22. To control the communication between thefluid-admitting means 20 and the fluid-collecting chambers 21' and 22,,normally-closed flow-control valves 74-76 of a similar or identicaldesign are arranged respectively in the flow line 76) and in the branchconduits 72 and 73 leading to the sample chambers. For reasons whichwill subsequently be described in greater detail in explaining themethods and apparatus of the present invention a normally-open controlvalve 77 which is similar to the normally-closed control valves 776 iscooperatively arranged in a branch conduit 7% for selectivelycontrolling communication hetween the well bore fluids exterior of thetool i and the upper portion of the flow line 7% extending .veen theflow-line control vmve 74 and the fluidadmitting means 2 1 Asillustrated, the control valve 77 employed in the present invention iscomprised ol'a valve body 7? cooperatively carrying a typical. pistonactuator which is normally biased to an elevated position by a springfill of a predetermined strength. A valve member 32 coupled to thepiston actuator 30 is cooperatively arranged for blocking fluidcommunication between the inlet and outlet fluid ports of the controlvalve whenever the valve member is moved" to its lower position. Thecontrol valves id-76 are similar to the control valve 77 except that aspring of selected strength is respectively arranged in each fornormally biasing each of these valve members to a closed position Asshown in FIGS. Silt-2B5, a branch conduit $3 is coupled to the flow lineill at a convenient location between the sample chamber control valvesand "7c and the flow-line control valve 74, with this branch conduitbeing terminated at an expansion chamber dd a predetermined volume. Areduced-diameter displacement piston tlfi is operatively mounted in thechamber 843 and arranged to be moved between selected upper and lowerpositions therein by a typical piston actuator shown generally at he.Accordingly, it will be appreciated that upon movement or" thedisplacement pistonhS from its lower position as illustrated in Flt}. 2Ato an elevated or upper position, the combined volume of whatever fluidsthat are then contained in the branch conduit $35 as well as in thatportion of theflow line ill between the flow-line control valve 7d andthe sample chamber control valvesifi and 76 will be correspondinglyincreased.

As best seen in FlG. 2A, the preferred embodiment of the control system15 further includes a pump $7 that is coupled to a driving motor @tl andcooperatively arranged for pumping a suitable hydraulic fluid such asoil or the like from a reservoir 8% into a. discharge or outlet line 90.Since the tool lll is to be operated in well bores, as at ll, whichtypically contain dirty and usually corrosive fluids, the reservoir 89is preferably arranged to totally immerse the pump i557 and the motor ddinthe clean hydraulic fluid. inasmuch as the formation-testing tool it)must operate at extreme depths, the reservoir 89 is provided with aninlet hi for well bore fluids and an isolating piston 92 is movablyarranged in the reservoir for maintaining the hydraulic fluid containedtherein at a pressure about equal to the hydrostatic pressure atwhatever depth the tool is then situated. A spring 93 is arranged to acton the piston 92 for maintaining the pressure of the hydraulic fluid inthe reservoir @9 at an increased level slightly above the well returninghydraulic fluid from the control system E to the reservoir 89 during theoperation of the tool ill.

The fluid outlet line is divided into two major branch lines which arerespectively designated as the "set line and the retract" line 97To'control the admission of hydraulic fluid to the Wet and r mit-actlines or and W7, a pair oi nationally-closed solenoid actuated valveelid and w are coop-crntiveiy arranged to selectively admit hydraulicfluid to the two lines as the control switch 23 at the surface ismlectively pcsitioned; and a typical checlt valve Mill) is arranged inthe "set" line 96 downstream of the control valve 9% for preventing thereverse flow of the hydraulic fluid when ever the pressure in the setline is greater than that then existing in the fluid outlet line no.Typical pressure switches lull-E03 are cooperatively arranged in the"set" and "retract" lines an and @7 for aelectively diecontinuingoperation ot' the pump ti? whenever the pressure of the hydraulic fluidin either of these lines reaches a desired operating preasure and thenrestartl5 in; speed. Accordingly. the control tyrtem i5 is coop- ZJeratively arranged no that each time the pump $7 is to be started. thecontrol valve W (if it is not already open) as well as a thirdnormally-closed solenoidactuated valve 3% will be temporarily opened tobypass hydraulic fluid directly from the output line W to the reservoir89 by way of the return line 94. Once the motor 88 has reached operatingspeed, the bypass valve 104 will, of course, be recloaed and either theset" line control valve 98 or the retract" line control valve 99 will beselectively opened as required for that particular operational phase ofthe tool it). It should be noted that during those times that the"retract" line control valve 99 and the fluid-bypass valve lllll areopened to allow the motor 8% to reach its operating speed, the checkvalve RM will function to prevent the reverse flow of hydraulic fluidfrom the set" line when the "set" line control valve 9% is open.

Accordingly. it will be appreciated that the control system cooperatesfor selectively supplying pre sured hydraulic fluid to the set" andretract" lines up and 97. Since the pressure switches lfll and 102respectively function only to limit the pressures in the set" andretrmf' lines to a selected maximum preesure range commensurate with therating of the pump 87, the new and improved control system id is furtherarranged to cooperatively regulate the pressure of the hydraulic fluidwhich is being supplied at various times to selected portions of thesystem. Although this regulation can be accomplished in difl'crentmanners, it IS preferred to employ a number of pressure-actuated controlvalves such as shown schematically at 105-108 in FIGS. 2A and 2B. Asshown in H6. 2A. the control valve I05, for example, includes a valvebody I09 having a valve seat lltl coaxially arranged therein betweeninlet and outlet fluid ports. The upper portion of the valve body W9 isenlarged to provide a piston cylinder Ill carrying an actuating pistonH2 in coincidental alignment with the valve seat Hill. A spring ll} of apredetermined strength is arranged for normull y urging the actuatingpiston ill toward the valve seat lid and a control port lid is providedfor admitting hydraulic fluid into the cylinder ill at a sufi'rcicntpressure to overcome the force or this whene the P it to be eeloctivelymoved nwny from the vnlve seet- Eiuce the control system id operates atpremuret fi lees than the hydrostatic pressure of the well bore fluhrelief port M5 is provided in the valve body W for communicating thespace in the cylinder ill above the actuating piston Hi2 with thereeervoir 89. A valve monitor lid complcrnentally shaped for seatingengagement with the valve seat lid is cooperatively coupled to th:actuating piston Hi2 as by an upright stern ll? which is slidablydisposed in an axial bore lid in the piston. A spring lid oi selected stength is disposed in the axial bore lid for normally urging the valvemember said enclosed into seating engagement with the valve seat lid.

Accordingly, in its operating position depicted in Flt]. 2A., thecontrol valve W5 (as well as; the valve Mid) will simply function as anormally closed check valve. This is to say. in this operating position.hydraulic fluid can flow only in a reverse direction whenever thepressure at the valve outlet is sufficiently greater than the inletpreesurc to elevate the valve member l lti from the valve seat lidagainst the predetermined clue ing force preatureactuated by the springH9. 0n the other hand. when sufficient fluid prertaure is applied to thecontrol port lid for elevating the actuating piston. oppoeed shoulders,at at lZti, on 23 the stern ii"? and the piston H2 will engage forelevating the valve membet llti from the valve seat lid.

As shown in HUS. 2A and 2%, it will be appreciated that the controlvalve ill? (at well an the valve 3%) is similar to the control valve ratexcept that in the firetrnentioned control valve, the valve member lZlis prelerably rigidly coupled to its associated actuating piston H22.Thus, the control valve 107 (as well as the valve Mid) has no alternatechecking action allowing reverse flow and is simply a normally-clonedpressure-actuated valve for selectively controlling fluid communicationbetween its inlet and outlet ports. lrlereagain. the hydraulic pressureat which the control valve W? (as well as the valve W8) is toselectively open is go erned by the predetermined strength ot" thespring H3 normally biasing the valve member to its closed position.

The set line downstream of the check valve llltll is comprised of alow-pressure section we having one branch 125 coupled to the fluid inletof the control valve Hi7 and another branch lilo which is coupled to thefluid inlet of the control valve lil to selectively supply hydraulicfluid to a high-presume section ll? of the set" line which is itselftermnated at the fluid inlet of the control valve E08. lo regulate thesupply oi hydraulic fluid from the low-pressure section lid to thehigh-pressure section l2? of the set" line 96, a pressure-communicatingline i253 s coupled between the low-pressure section and the control rtofthe control valve 105. Accordingly so long 25 t. e pressure of thehydraulic fluid in the low-pressure section of the set" line remainsbelow the redctermined actuating pressure required to open t e controlvalve N5, the high-pressure section 127 will b:- isolatcd from thelowpressure section l24. Conversely. once the hydraulic preasure in thelow-pressure line KM reaches the predetermined actuating prcssure of thevalve W53 the control valve will open to admit the hydraulic fluid intothe high-pressure line E27.

The control valves 107 and W8 are respectively arranged to selectivelycommunicate the low-pressure and high-pressure sections llZd and 127 ofthe {Hit line 96 with the fluid reservoir kil s. To accomplish this, thecontrol ports of the two control valves 107 and litltl are eachconnected to the retract" line 97 by suitable pressure-communicatinglines i239 and lii ll. Thus, whenever the pressure in the retract line97 reaches their respective predetermined actuating levels, the controlvalves 107 and N8 will be respectively opened to selectively communicatethe two sections 7124 and 127 of the set" line with the reservoir 8% byway of the return line 96 coupled to the respective outlets of the twocontrol valves.

As previously mentioned, in FlGS. ZA-ZB the tool ill and the sub-surfaceportion of the control system l are depicted as their several componentswill appear when the tool is retracted. At this point, the wallengagingmember 38 and the sealing pad ll are respectively retracted against thetool body E8 to facilitate passage of the tool 10 into the borehole ll.To prepare the tool Ill) for lowering into the borehole ill, theswitches 23 and 24 are moved to their second or initialization positions26. At this point, the hydraulic pump $7 is started to raise thepressure in the retract line 97 to a selected maximum to be certain thatthe pad 41 and the wall-engaging member 3% are fully retracted. Aspreviously mentioned, the control valves W and 104 will be momentarilyopenedwhen the pump 87 is started until the pump motor 88 has reachedits operating speed. At this time also, the control valve '77 is openand that portion of the flow line '70 between the closed flow-linecontrol valve 74 and the fluidadmitting means 20 will be filled withwell bore fluids at the hydrostatic pressure at the depths at which thetool 10 is then situated.

When the tool it) is at a selected operating depth, the switches 23 and24 are advanced to their third positions 27. Then, once the pump $7 hasreached its rated operating speed, the hydraulic pressure in the outputline 90 will rapidly rise to its selected maximum operating pressure asdetermined by the maximum or off setting of the pressure switch W1. Asthe pressure progressively rises, the control systems will successivelyfunction at selected intermediate pressure levels forsequentiallyoperating the several control valves 395-108 as describedfully in the aforementioned copending application, Ser. No. 313,235. v

Turning now to FIG. 3., selected portions of the control system 15 andvarious components of the tool iii are schematically represented toillustrate the operation of the tool at about the time that the pressurein the hydraulic output line 90 reaches its lowermost intermediatepressure level. To facilitate an understanding of the operation of thetool It) and the control system 15 at this point in its operating cycle,only those components which are then operating are shown in FIG. 3.

At this time, since the control switch 23 (FIG. 1) is in its thirdposition 27, the solenoid valves 98 and We will be open; and, since thehydraulic pressure in the set" line 96 has not yet reached the upperpressure limit as determined by the pressure switch lllll, the pumpmotor 88 will be operating. Since the control valve H05 (not shown inH0. 3) is closed, the highpressure section 127 of the set line 96 willstill be iso lated from the low-pressure section 11%. Simultaneously,the hydraulic fluid contained in the forward pressure chambers of thepiston actuators 3%, d0, d3

and dd will be displaced (as shown by the arrows as at Ellill) to theretract linefl' l and returned to the reservoir 39 by way of the opensolenoid valve res. These actions will, of course, cause thewall-engaging member Bill as well as the sealing pad dl to berespectively extended in opposite lateral directions until each hasmoved into iirm engagement with the opposite sides of the borehole ll.

it will be noticed in FlG, 3 that hydraulic fluid will be admitted byway of branch hydraulic lines i332 and 33 to the enclosed annularchamber 53 to the rear of the enlargeddiameter portion 52 of theiluid-admitting member 55. At the same time, hydraulic liuid from thepiston chamber 54 ahead of the enlarged-diameter postion 52 will bedischarged by way of branch hydraulic lines 11% and 113.55 to theretract line all for progres sively moving the lluid adrnitting member55 forwardly in relation to the sealing member ill until the nose of thefluid-admitting member 35 engages the wall of the borehole iii and thenhalts. The sealing pad 4i is then urged forwardly in relation to thenow-halted tubular member until the pad sealingly engages the boreholewall for packing-oi? or isolating the isolated wall portion from thewell bore fluids.

it should also be noted that although the pressured hydraulic fluid isalso admitted at this time into the "forward piston chamber as betweenthe sealing members d2 and 6 on the valve member 55, the valve member istemporarily prevented from moving rcarwardly in re lation to the innerand outer tubular members 4;? and inasmuch as the control valve (notshown in H61. 3) is still closed thereby temporarily trapping thehydraulic fluid in the rearward piston chamber as to the rear of thevalve member. The significance of this delay in the retraction of thevalve member 1% will be subsequently explained.

As also illustrated in FIG. 3, the hydraulic fluid in the low-pressuresection 12% of the set line as will also be directed by way of a branchhydraulic line lilo to the piston actuator $6, This will, of course,result in the displacement piston rid being elevated as the hydraulicfluid from the piston actuator is returned to the retract line 97 by wayof a branch hydraulic conduit 137. As will be appreciated, elevation ofthe displace ment piston $5 in the expansion chamber M will be effective for significantly decreasing the pressure initially existing inthe isolated portions of the branch line $3 and the flow line betweenthe still-closed flow-line control valve 74 and thestill-closed chambercontrol valve 75 and re (not seen in FlG. 3). The purpose of thispressure reduction will be subsequently explained.

H6. 3, it will be appreciated that the hydraulic pres sure delivered bythe pump 87 will again rise. Then, once the pressure in the output line9% has reached its second intermediate level of operating pressure, thecontrol valve 106 will open in response to this pressure level to nowdischarge the hydraulic fluid previously trapped in the piston chamber6:3 to the rear of the valve member 55 back to the reservoir 8i Asillustrated, in FIG. 4, once the control valve the opens, the hydraulicfluid wil be displaced from the rearward piston chamber 65 by way ofbranch hydraw lic lines lfih, 139 and 35 to the retract" line til? aspressured hydraulic fluid from the set line 55b surges into the pistonchamber on ahead of the enlargeddiameter portion tSl of the valve member555. This will, of course, cooperate to rapidly drive the valve member55 rearwardly in relation to the now-halted fluidadmitting member 45 forestablishing fluid or pressure communication between the isolatedportion of the earth formation 12 and the flow passages $7 and so in thevalve member by way of the filter screen 6%.

Although this is not fully illustrated i, it will be recalled from FlGS.2A and 28 that the control valves 74-76 are initially closed to isolatethe lower portion of the flow line 7% between these valves as well asthe branch line 83 leading to the pressures-reduction chamber as.However, in keeping with the principles of the present invention, theflowline pressure-equalizing control valve 77 will still be open at thetime the control valve W6 opens to retract the valve member 55 asdepicted in FIG. 4. Thus, as the valve member progressively uncovers thefiltering screen as, well bore fluids at a pressure greater than that ofany connate fluids which may be present in the isolated earth formation12 will be introduced into the upper portion of the flow line 70 and, byway of the flexible conduit member 71, into the rearward end of thetubular member 58. As these high-pressure well bore fluids pass into theannular space 67 around the filtering screen 69, they will be forciblydischarged (as shown by the arrows Mil) from the forward end of thefluid-admitting member 35 for washing away any plugging materials suchas mudcake or the like which may have become deposited on the internalsurface of the filtering screen when the valve member 55 fitst uncoversthe screen. Thus, to attain the objects of the present invention, thecontrol system 15 is operative for providing a momentary outward surgeor reverse flow of well bore fluids for cleansing the filtering screen69 of unwanted debris or the like before a sampling or testing operationis commenced.

It will be appreciated that once the several components of theformation-testing tool it) and the control system 15 have reached theirrespective positions as depicted in H6. 4, the hydraulic pressure in theoutput line 90 will again quickly increase to its next intermediatepressure level. Once the pump 87 has increased the hydraulic pressure inthe output line 2% to this next predetermined intermediate pressurelevel, the control valve l05 will selectively open as depicted in H6.5A. As seen there, opening of the control valve 105 will be effectivefor now supplying hydraulic fluid to the highpressure section 127 of theset" line 96 and two branch conduits M1 and M2 connected thereto forsuccessively closing the control valve 77 and then opening thecontrolvalve 74L In this manner, as depicted by the several arrows at 143 and144, hydraulic fluid at a pressure representative of the intermediateoperating level will be supplied by way of a typical check valve 145 tothe upper portion of the piston cylinder ms of the normally-open controlvalve 77 as fluid is exhausted from the lower portion thereof by way ofa conduit M7 coupled to the retract" line 97. This will, of course, beeffective for closing the valve member 82 so as to now block furthercommunication between the flow line 70 and the well bore fluids exteriorof the tool lb. Simultaneously, the hydraulic fluid will also beadmitted into the lower portion of the piston cylinder Mb of the controlvalve 7d.

By arranging the biasing spring bl for the normallyopen control valve 77to be somewhat wealter than the biasing spring M9 for thenormally-closed control valve 74., the second valve will be momentarilyretained in its closed position until the first valve has had time toclose. Thus, once the valve 77 closes, as the hydraulic iluid enters thelower portion of the piston chamber of the control valve 7d, the valuemember lfill'will be owned as hydraulic fluid is exhausted from theupper portion of the chamber through a typical check valve 15R and abranch return line l2 coupled to the retracd line 97.

it will be appreciated therefore, that with the tool in the positiondepicted in FlGS. 5A and 5B, the flow line Ill is now isolated from thewall bore lluids and is in communication with the isolated portion ofthe earth formation H by way of the flexible conduit 7t. it will also berecalled from the preceding discussion of 3 that the branch flow line $3as well as the portion of the main flow line 7tl between the flow -linecontrol valve 7 and the sample chamber control valves 75 and werepreviously expanded by theupward movement of the displacement piston $5in the reduced-volume chamber as. Thus, upon opening of the flow-linecontrol valve 74, the isolated portion of the earth forrnation 3.22 willbe communicated with the reducedpressure space represented by thepreviously-isolated portions of the flow line and the branch conduit 83.

Of particular interest to the present invention, it should be noted thatshould the formation 12 be relatively unconsolidated, the rearwardmovement of the valve member 55 in cooperation with the forward movementof the fluid-admitting member &5 will allow only those loose formationmaterials displaced by the advancement of the fluid-admitting memberinto the formation to enter the fluid-admitting member. This is to say,the fluid-admitting member 35 can advance into the formation l2 only bydisplacing loose formation materials; and, since the space opened by therearward displacement of the valve member is the only place into whichthe loose formation materials can enter, ther erosion of the formationmaterials will be halted once the fluid-admitting member has been tilledwith loose materials as shown in l-lG. db. On the other band, should aformation interval which is being tested be relatively well-compacted,the advancement of the fluidadmitting member 45 will be relativelyslight with its nose making little orno penetration into the isolatedearth formation. lt will, of course, be appreciated that the nose of thefluid-admitting member d5 will be urged outwardly with sufficient forceto at least penetrate the mudcalce which typically lines the boreholewalls adjacent to permeable earth formations. in this situation,

however, the forward movement of the fluid-admitting member 45 will beunrelated to the rearward movement of the valve member 55 as itprogressively uncovers the filtering screen 69. in either case, thesudden opening of the valve 74 will cause mudcake to be pulled to therear of the screen d9 to leave it clear for the subsequent passage ofconnate fluids.

AS best seen in FlGS. 5A and 58, therefore, should there be anyproducible connate fluids in the isolated earth formation 12, theformation pressure will be effective for displacing these connate fluidsby way of the fluid-admitting means 20 into the flow line until suchtime that the lower portion of the flow line 7b and the branch conduit83 are filled and pressure equilibrium is established in the entire flowline. By arranging a typical pressure-measuring transducer, as at 153(or, if desired, one or more other suitable transducers) in the flowline 70, one or more measurements representative of the characteristicsof the connate fluids and the formation 12 may be transmitted to thesurface by a conductor 154 and, if desired, recorded on the recordingapparatus 16 (FIG. l). The pressure measurements provided by thetransducer 153 will, of course, permit the operator at the surface toreadily determine the formation pressure as well as to obtain one ormore indications representative of the potential producing ability ofthe formation 12. The various techniques for analyzing formationpressures as well known in the art and are, therefore, of nosignificance to understanding the present invention.

It will be recognized, of course, that by virtue of the purging actionwhich was previously provided by the outflowing well bore fluids in thepractice of the pres ent invention, there is a reasonable assurance thatthe filtering screen 69 will have been cleared of plugging materialssuch as mudcake of formation materials that may otherwise plug thefluid-admitting means 20. However, the sudden introduction of connatefluids into the flow line 70 will also be effective for clearing thescreen 69 of residual plugging materials.

The measurements provided by the pressure transducer 153 at this time'will indicate whether the sealing pad 41 has'fin fact, establishedcomplete sealing en'- gagement with the earth formation 12 inasmuch asthe expected formation pressures will .be recognizably lower than'thehydrostatic pressure of the well bore fluids at the particular depthwhich the tool 10 is then situated. This ability to determine theeffectiveness of the sealing engagement will, of course, allow theoperator to retract the wall-engaging member 38 and the sealing pad 41without having to unwittingly or needlessly continue the remainder ofthe complete operating sequence.

Assuming, however, that the pressure measurements provided by thepressure transducer 153 show that the sealing pad 41 is firmly seated,the operator may leave the formation-testing tool 10 in the positionshown in FlGS. A and 58 as long as it is desired to observe as well asrecord the pressure measurements. As a result,

the operator can determine such things as the time required for theformation pressure to reach equilibrium as well as the rate of increaseand thereby obtain valu able information indicative of variouscharacteristics of the earth formation 12 such as permeability andporosity. Moreover, with the new and improved tool 10, the operator canreadily determine if collection of a fluid sample is warranted.

Once the several components of the tool and the control'system 15 havemoved to their respective positions shown in FIGS. 5A and 5B, thehydraulic pressure will again rise until such time that the setlinepressure switch 101 operates to halt the hydraulic pump 87. Inasmuch asthe pressure switch 101 has a selected operating range, in the typicalsituation the pump 87 will be halted shortly after the control valve 77closes and the control valve 74 opens. At this point in the operatingcycle of the tool it), once a sufficient number of pressure measurementshave been obtained, a decision can be made whether it is advisable toobtain one or more samples of the producible connate fluids present inthe earth formation 112. If such samples are not desired, the operatorcan simply operate the "control switches 23 and 24 for retracting thewall-engaging member 33 as well as the sealing pad 4i without furtherado.

On the other hand, should a fluid sample be desired, the controlswitches 23 and 24 (FIG. l) are advanced to their next or so-called"sample" positions 28 to open, for example, a solenoid valve l5 (FIG.2B) for coupling pressured hydraulic fluid from the highpressure section127 of the set litie 96 to the piston actuator 156 of the sample chambercontrol valve V55. This will, of course, be effective for opening thecontrol valve 75 to admit connate fluids through the flow line "70 andthe branch conduit 72 into the sample chamber 21. if desired, a chamberselection" switch E57 in the surface portion of the system 15 could alsobe moved from its first sample position ih to its so-called secondsample position 115% (l ltii. l) to energize a solenoid valve loll (FIG.2B) for opening the control valve '76 to also admit connate fluids intothe other sample chamber 22. In either case, one or more sampies of theconnate fluids which are present in the iso lated earth formation 12 canbe selectively obtained by the new and improved tool it).

Upon moving the control switches 23 and 24 to their so-calledsample-trapping positions 29, the pump $7 will again be restarted. Oncethe pump 3'7 has reached operating speed, it will commence to operatemuch in the same manner as previously described and the hydraulicpressure in the output line ll will begin rising with momentary halts atvarious intermediate pressure levels.

Accordingly, when thecontrol switches 23 and 24 have been placed intheir sample trapping" positions 29, the solenoid valve W will open tonow admit hydraulic fluid into the retract line 9'7. By means of theelectrical conductor lllfia (PEG. it however, the pressure switch W3 isenabled and the pressure switch it'iZ is disabled so that in thisposition of the control switches 23 and 24 the maximum operatingpressure which the pump 87 can initially reach is limited to the @Q, thepressure in this portion of the set line will be rapidly decreased toclose the control valve 195 once the pressure in the line isinsufficient to hold the valve open. Once the control valve W5 closes,the pressure remaining in the low-pressure section E24 of the set line96 will remain at a reduced pressure which is nevertheless effective forretaining the wall-engaging member 38 and the sealing pad 41 fullyextended.

As the hydraulic fluid is discharged from the lower portion of thepiston actuator 11% by way of the stillopen solenoid valve and fluidfrom the .retract" line 97 enters the upper postion of the actuator byway of a branch line 16H, the chamber control valve "i will close totrap the sample of connate fluids which is then present in the samplechamber 2i. Similarly, should there also be a fluid sample in the othersample charm ber 22, the control valve 76 can also he readily closed byoperating the switch 157 to reopen the solenoid valve 160. Closure ofthe control valve (as well as the valve 76) will, of course, beeffective for trapping any fluid samples collected in one or the otheror both of the sample chambers 21 and 22-.

Once the control valve 75 (and, if necessary, the control valve '76) hasbeen reclosed, the control switches 23 and 24 are moved to their next orso-called retract switching positions 3% for initiating the simultaneousretraction of thewall-engaging member 38 and the sealing pad ll. in thisfinal position of the control switch 24, the pressure switch 103 isagain rendered inoperative and the pressure switch W2 is enabled so asto now permit the hydraulic pump $7 to be operated at full ratedcapacity for attaining hydraulic pressures greater than the firstintermediate operating level in the retract" cycle. Once the pressureswitch W3 has again been disabled, the pressure switch M2 will nowfunction to operate the pump d7 so that the pressure will now quicklyrise until it reaches the next operating leveL- At this point, hydraulicfluid will be supplied through the retract line 97 and the branchhydraulic line lid? for reopening the pressure-equalizing control valve7'7 to admit well bore fluids into the flow line 7d. Opening of thepressure-equalizing valve 77 will admit well bore fluids into theisolated space defined by the sealing pad 41 so as to equalize thepressure differential existing across the pad. Hydraulic fluid displacedfrom the upper portion of the piston chamber M6 of the control valve'7'7will be discharged through a typical relief valve lei which is arrangedto 'open'only in response to pressures'equal or greater than that ofthis-present operating level. The hydraulic fluid displaced from thepiston chamber l46 through the relief valve ldl will be returned to thereservoir 89 by way of the branch hydraulic line 141, the high-pressuresection E27 of the set" line 96, the still-open control valve idli, andthe return line 94.

When the hydraulic pressure in the output line 90 has either reached thenext operating level or, if desired, a still-higher level, pressuredhydraulic fluid in the retract line 97 will reopen the controlvalve 107to communicate the low-pressure section H24 of the set" line 96 with thereservoir 89. When this occurs, hydraulic fluid in the retract" linewill be admitted to the retract side of the several piston actuators 39,40, 43 and 44. Similarly, the pressured hydraulic fluid will also beadmitted into the annular space 54 in front of the enlarged-diameterpiston portion 52 for retracting the fluid-admitting member 45 as wellas into the annular space 66 for returning the valvemember 55 to itsforid 3.51 is held in a closed position until the increasing hydraulicpressure developed by the pump 37 exceeds the operating level used toretract the wall-engaging mem fill and the sealing pad dl. At this pointin the operating sequence of the new and improved tool iii, theflow-line control valve "7d will be reclosed.

The pump 8? will, of course, continue to operate until such time thatthe hydraulic pressure in the output line 98? reaches theupper limitdetermined by setting oi the pressure switch W2, At some convenient timethereafter, the control switches 23 and M are again returned to theirinitial or of? positions E for halting further operation of the pumpmotor d5) as well as reopening the solenoid valve 1% to againcommunicate the retract" line F7 with the fluid reservoir 89. Thiscompletes the operating cycle of the new and improved tool ill.

Referring again to ilG. d, it will be appreciated that the new andimproved methods of the present invention will assure that communicationwill be established between the flow line 76 and the formation, as atE2, before any measurements or samples are taken. For example, shouldthe interior surface of the filtering screen become unduly coated withparticles of the relatively-imperrneable mudcalte as the valve membermoves to its rearward position, opening of the valve member will beeffective for developing a significant reverse flow of thehigher-pressure well bore fluids through the screen 69 and into thelower-pressure formation 12. Similarly, should extremely-fine particlesof sand or the like from the formation l2 be lodged against the interiorsurfaces of the filter medium as, this reverse flow of well bore fluidswill be effective for cleansing the filter before any tests are made.

Accordingly, in keeping with the objects of the present invention, sincethe control valve 77 is open to admit well bore fluids into the upperportion of the flow line '70, when the valve memmr 55 is opened thefiltering screen M will be thoroughly cleansed by the outward surge ofwell bore fluids. Thus, when the formation 12 is subsequentlycommunicated with the re duced or atmospheric pressure initially presentn the ward position. The hydraulic fluid exhausted from the severalpiston actuators 39, 40, 43 and 44 as well as the piston chambers 54 and66 will be returned directly to the reservoir 89 by way of thehigh-pressure section 124 of the set" line 96 and the control valve 107.This action will, of course, retract the wall-engaging member 38 as wellas the sealing pad 4i against the tool body 18 to permit the tool 10 tobe either repositioned in the well bore ll or returned to the surface ifno further testing'is desired.

it should be noted that although there is an operating pressure appliedto the upper portion of the piston cylinder 148 for the flow-linecontrol valve 74 at the time that the control valve 77 is reopened, anormally-closed relief valve M52 which is paralleled with the checkvalve previously-isolated lower portion of the flow line 7%, producibleconnate fluids in the isolated portion of the formation will be drawninto the flow line. it will, of course, be recognized that if, on theother hand, there are no producible connate fluids in the formation 12,the pressure readings provided by the transducer E53 will simplyindicate little or no pressure rise in the flow line '70. in eithercase, the operator at the surface will be reliably assured that afailure to obtain a significant pressure increase in the flow linemeasurements is in fact caused by a non-producible formation and is notunknowingly attributed to a tightly-plugged filter screen 69 instead.Moreover, the new and improved methods of the present invention are ofequal advan tage when a sample of connate fluids is to be taken as well.Thus, instead of obtaining little or no flow of fluid which would occurwith at least a partially-blocked screen as, the reverse flushing of thefilter will assure the operator that the screen is clean so thatformation fluids are free to flow into the tool M; This can clearlyreduce the time required to perform a typical testing operation.

While only a particular embodiment of the present invention and one modeof practicing the invention have been shown and described, it isapparent that changes and modifications may be made without departingfrom this invention in its broader aspects; therefore, the aim in theappended claims is to cover all such changes and modifications as fallwithin the true spirit and scope of this invention.

What is claimed is: l. A method for testing earth formations traversedby a well bore and comprising the steps of:

engaging fluid-admitting means coupled by a fiitering medium to a fluidpassage against a waii surface of said well bore adjacent to an earthformation be lieved to contain producibie connate fluids for isolatingsaid wall surface from fluids in said weii bore and placing saidfluid-admitting means in position for receiving connate fluids from saidearth formation; discharging said well bore fluids from said fluidpassage in a reverse direction through said filtering medium and intosaid fluid-admitting means and said earth formation for cleansing saidfiltering medium; and, thereafter, communicating said fluid passage withan enclosed chamber initially at a reduced pressure for drawingproducible connate fluids from said earth formation and in the oppositedirection through said filtering medium and into said fluid passage toobtain a filtered sample of said connate fluids in said enclosedchamber. 2. The method of claim 1 further including the additional stepof:

measuring the pressure in saidenclosed chamber and said fluid passagefor obtaining at least one pressure measurement indicative of at leastone characteristic of said earth formation. 3. The method of claim 1further including the additional steps of:

monitoring at least one characteristic of said filtered sample drawninto said fluid passage for obtaining a series of measurementsrepresentative of the production characteristics of said earthformation; and, thereafter, discontinuing further communication betweensaid fluid passage and said enclosed chamber for trapping said filteredsample therein. 4. The method of claim 1 further including theadditional steps of:

monitoring at least one characteristic of said filtered sample drawninto said fluid passage for obtaining a series of measurementsrepresentative of the production characteristics of said earthformation; and, thereafter, expelling said filtered sample from saidenclosed chamber. 5. A method for testing earth formations traversed bya well bore and comprising the steps of:

urging fluid-admitting means including a normallyclosed fluid-samplingmember coupled by a filtering medium to a fluid passage into sealingengagement with a wall surface of said well bore adjacent to an earthformation believed to contain producible connate fluids for isolatingsaid wall surface from fluids in said well bore and placing saidfluidsampling member in position for subsequently communicating withsaid earth formation; opening said fluid-sampling member and admittingsaid well bore fluids into said fluid passage for passing said wellborefluids through said filtering meiii dium and said fluid-sampling memberinto said earth formation to cleanse said filtering medium sand saidfluid-sampling member of potentiallyplugging materials; closingcommunication between said weli bore fluids and said fluid passage; and,thereafter, coupling an enclosed reduced-pressure chamber to said fluidpassage for drawing producibie con'nae fluids from said earth formationthrough said sampling member and said filtering medium and into saidfluid passage to obtain a filtered sarnpie of said connate fluids insaid enclosed chamber. ti. The method of claim 5 further inciuding theadditional step of:

uncoupling said enclosed chamber from said fluid passage for collectingsaid fiitered sample. 7. The method of claim 5 further including theadditional steps of:

monitoring the pressure in said fluid passage for obtaining a series ofpressure measurements represen tative of the production characteristicssaid earth formation; and uncoupling said enclosed chamber from saidfluid passage for collecting said fi tered sample in said enclosedchamber. d. The method of claim 5 further including the additional stepsof:

monitoring the pressure in said fluid passage for obtaining a series ofpressure measurements representative of the production ci'zaracteristicsof said earth formation; expelling said filtered sampie from saidenciosed chamber and uncoupling saidenciosed chamber from said fluidpassage; reclosing said fluid-sampling member; reducing the pressure insaid enclosed chamber; removing said fluid-admitting means from saidwall surface and urging said fluid-admitting means into sealingengagement with another waii surface of said well bore adjacent toanother earth formation believed to contain producible connate fluidsfor isolating said other wall surface from said weil bore fluids andplacing said fluid-sampling member in position for subsequentlycommunicating with said other earth formation; re-opening saidfluid-sampling member and readmitting said well bore fluids into saidfluid passage for passingsaid well bore fluids through said filteringmedium and said fluid-sampling member into said other earth formation torecleanse said filtering medium and said fluid-sampling member-ofpotentially-plugging materials; reclosing communication between saidwell bore fluids and said fluid passage; recoupling said enclosedchamber to said fluid passage for drawing producible connate fluids fromsaid other earth formation through said fluidsampling member and saidfiltering medium and into said fluid passage to obtain a filtered sampleof said connate fluids from said other earth formation in said enclosedchamber; and. remonitoring the pressure in said fluid passage forobtaining a second series of pressure measurements representative of theproduction characteristics of said other earth formation. 9. The methodof claim 5 further including the additional steps of:

monitoring the pressure in said fluid passage for obtaining a series ofpressure measurements representative of the production characteristicsof said earth formation;

coupling a sample receiver at a reduced pressure to said fluid passagefor collecting filtered connate fluids from said earth formation in saidsample receiver;

closing said sample receiver for entrapping connate fluids collectedtherein;

expelling said filtered sample from said enclosed chamber and uncouplingsaid enclosed chamber from said fluid passage;

reclosing said fluid-sampling chamber;

removing said fluid-admitting means from said wall surface and urgingsaid fluid-admitting means into sealing engagement with another wallsurface of said well bore adjacent to another earth formation believedto contain producible connate fluids for isolating said other wallsurface from said well bore fluids and placing said fluid-samplingmember in position for subsequently communicating with said other earthformation;

re-opening said fluid-sampling member and re admitting said well borefluids into said fluid passage for passing said well bore fluids throughsaid filtering medium and said fluid-sampling member into said otherearth formation to recleanse saidfiltering medium and saidfluid-sampling member of potentially-plugging materials;

reclosing communication between said well bore fluids and said fluidpassage;

recoupling said enclosed chamber to said fluid passage for drawingproducible connate fluids from said other earth formation through saidfluidsampling member and said filtering medium and into said fluidpassage to obtain a filtered sample of said connate fluids from saidother earth formation in said enclosed chamber; and

remonitoring the pressure in said fluid passage for obtaining a secondseries of pressure measurements representative of the productioncharacteristics of said other earth formation.

10. The method of claim 9 further including the additional step of:

following the remonitoring step, coupling a second sample receiver at areduced pressure to said fluid passage for collecting filtered connatefluids from said other earth formation in said second sample receiver;and I closing said second sample receiver for entrapping connate fluidscollected therein.

11. The method of claim further including the additional steps of:

monitoring the pressure in said fluid passage for obtaining 21 series ofpressure measurements representative of the production characteristicsof said earth formation;

expelling said filtered sample from said enclosed chamber and uncouplingsaid enclosed chamber from said fluid passage;

reclosing said fluid-sampling member;

reducing the pressure in said enclosed chamber;

removing said fluid-admitting means from said wall surface and urgingsaid fluid-admitting means into sealing engagement with another wallsurface of said well bore adjacent to another earth formation believedto contain producible connate fluids for isoiating said other wailsurface fromsaid well bore fluids and placing said fluid-samplinggiember in position for subsequently communicating with said 7 otherearth formation;

re-opening said fluid-sampling member and readmitting said well borefluids into said fluid passage for passing said weil bore fluids throughsaid filtering medium and said fluid-sampling member into said otherearth formation to recleanse said Hi tering medium and saidfluid-sampling member of potentially-plugging materials;

reclosing communication between said well bore fluids and said fluidpassage;

recoupling said enclosed chamber to said fluid pas sage for drawingproducible connate fluids from said other earth formation through saidfluid sampling member and said filtering medium and into said fluidpassage to obtain a filtered sample of said connate fluids from saidother earth formation in said enclosed chamber;

remonitoring the pressure in said fluid passage for obtaining 'a secondseries of pressure measurements representative of the productioncharacterisby a well bore and comprising the steps of:

urging fluid-admitting means including a fluid passage coupled by afiltering medium to a fluidsampling member having a normally-closedforward end and a rearward portion to the rear of said filtering mediuminto sealing engagement with a wall surface of said well bore adjacentto an earth formation believed to contain producible connate fluids forisolating said wall surface from fluids in said well bore and placingsaid closed end of said fluid-sampling member into position forsubsequently receiving connate fluids from said earth formation;

opening said normally-closed forward end of said fluid-sampling memberand admitting said well bore fluids into said fluid passage for passingsaid well bore fluids through said filtering medium and saidfluid-sampling member into said earth formation to cleanse saidfiltering medium and said fluidsampling member of potentially-pluggingmaterials;

closing communication between said well bore fluids and said fluidpassage;

expanding the volume of an enclosed test chamber coupled to said fluidpassage downstream of said filtering medium for reducing the pressure insaid fluid passage and said test chamber to about atmospheric pressure;

after said test chamber is expanded, coupling said test chamber to saidfluid passage at a speed sufficient to quickly induct a filtered sampleof producible connate fluids from said earth formation into saidexpanded test chamber for momentarily reducing the pressure of saidconnate fluid sample to about atmospheric pressure and displacing looseplugging materials from said wall surface into said rearward portion ofsaid fluidsampiing member to the rear of said filtering medium; and

monitoring the pressure in said expanded test chamber for obtaining aseries of pressure measurements indicative of the productioncapabilities of said earth formation.

13. The method of claim l2 further including the additional step of:

recording said pressure measurements for obtaining a recordrepresentative of the pressure characteristics of said earth formationas connate fluids are produced therefrom. 14. The method of claim l2further including the additional step of:

after the pressure-monitoring step, coupling an enclosed sample chamberto said fluid passage down stream of said filtering medium forcollecting another filtered sample of connate fluids from said earthformation. 15. The method of claim l2 further including the ad ditionalsteps of: s

after the pressure-monitoring step, reducing the volume of said testchamber for expelling said sample of connate fluids into said well bore;uncoupling said test chamber from said fluid passage;

reclosing said normally-closed forward end of said fluid-samplingmember;

re-opening said normally-closed forward end of said fluid-samplingmember and re-admitting said well bore fluids into said fluid passagefor again passing said well'bore fluids through said filtering mediumand said fluid-sampling member into said earth formation to recleansesaid filtering medium and said fluid-sampling member forpotentially-plugging materials;

reclosing communication between said well bore fluids and said fluidpassage;

re-expanding the volume of said test chamber for again reducing thepressure in said fluid passage and said test chamber to aboutatmospheric pressure;

after said test chamber is re-expanded, re-coupling said re-expandedtest chamber to said fluid passage at a speed sufficient to quicklyinduct a second filtered sample of producible connate fluids into saidre-expanded test chamber for momentarily reducing the pressure of saidsecond sample to about atmospheric pressure and displacing additionalloose plugging materials from said wall surface into said rearwardportion of said fluid-sampling member to the rear of said filteringmedium; and

re-monitoring the pressure in said re-expanded test chamber forobtaining a second series of pressure measurements indicative of theproduction capabilities of said earth formation.

16. The method of claim 35 further including the additional step of:

after obtaining said pressure measurements, coupling an enclosed samplechamber to said fluid passage downstream of said filtering medium forcollecting another filtered sample of connate fluids from said earthformation.

17. The method of claim l5 further including the additional steps of:

22 after ob a ning said pressure measurements, reducing the volume ofsaid test chammr again for expelling said second sample into said wellbore; reclosing said normally-closed forward end of said fluid-samplingmember; and disengaging said fluid-admitting means from said wallsurface. id. The method of claim l2 further including the additionalsteps of:

after the pressure-monitoring step, coupling an enclosed sample chamberto said fluid passage downstream of said filtering medium for collectingan other filtered sample of connate fluids from said earth formation;reducing the volume of said test chamber for expelling said sample ofconnate fluids into said well bore; uncoupling said test chamber fromsaid passage;

reclosing said normally-closed forward end of said fluid-samplingmember;

ire-expanding the volume of said test chamber for again reducing thepressure in said fluid passage and said test chamber to aboutatmospheric pressure;

disengaging said fluid-admitting means from said wali surface and urgingsaid fluid-admitting means into sealing engagement with another wallsurface of saidwell bore adjacent to another earth formation believed tocontain producible connate fluids for isolating said other wall surfacefrom said well bore fluids;

re-opening said normally-closed iorward end of said fluid-samplingmember and readmitting said well bore fluids into said fluid passage foragain passing said well bore fluids through said filtering medium andsaid fluid-sampling member into said other earth formation to recleansesaid filtering medium and said fluid-sampling member ofpotentiallyplugging materials;

reclosing communication between said weli bore fluids and said fluidpassage;

re-coupling said re-expanded test chamber to said fluid passage at aspeed sufficient to quickly induct a second filtered sample ofproducible connate fluids into said re-expanded test chamber formomentarily reducing the pressure of said second sample to aboutatmospheric pressure and displacing loose plugging materials from saidother wall surface into said rearward portion oisaidfluid-samplingmember to the rear of said filtering medium; and

re-monitoring the pressurein said re-expanded test chamber for obtaininga second series of pressure measurements indicative of the productioncapabilities of said other earth formation.

19. The method of claim l8 further including the additional steps of:

after obtaining said secondseries of pressure rneasurements, coupling anenclosed sample chamber to said fluid passage downstream for collectinganother sample of connate fluids from said other earth formation.

Ed. The method of claim iii further inciuding the ad ditional steps of:

after obtaining said second series of pressure measurements, reducingthe volume of said test chamher again for expelling said second sampleinto said sample-collecting means on said body including a well bore;sample chamber, and means selectively operable uncoupling said testchamber from said fluid passage; for coupling said sample chamber tosaid fluid passage to receive connate fluids entering saidfluidre-closing said normally-closed end of said fluidadmitting means.

sampling member; and 24. The formation-testing apparatus of claim 23furdisengaging said fluid-admitting means from said ther including:

other wall surface. pressure-measuring means adapted for providing an21. Formation-testing apparatus adapted for suspenindication of thepressure conditions in fluid sion in a well bore traversing earthformations and passage. comprising: I 2. The formation-testing apparatusof claim 23 fura body having a fluid passage adapted to receive contherincluding: I

nate fluids; pressure-reducing means on said body inciading anfluid-admitting means on said body including a fluidenclosed testchamber, and means selectively opersampling member having a forward endadapted to able for varying the volume of said test chamber beselectively engaged with a well bore wall for isoincluding piston meansmovable back and forth belating a portion thereof from well bore fluids,first tween 21 first position reducing the volume of said valve meansnormally closing said forward end of test chamber and a second positionsufficiently exsaid fluid-sampling member, and filtering means pendingthe volume of said test chamber to reduce coupling said fluid passage tosaid fluid-sampling the pressure in said test chamber to about atmomember to the rear of said first valve means; spheric pressure; means onsaid body and selectively operable for posipressure-measuring meansadapted for providing intioning said fluid-admitting means against awell dications representative of the pressure conditions bore wall toplace said fluid-sampling member in in said test chamber; andcommunication with earth formations beyond said 25 control meansselectively operable after movement well bore wall; and of said pistonmeans to said second position and incontrol means including second-valvemeans selec eluding third valve means for coupling said test tivelycoupling said fluid passage to the exterior of chamber to said fluidpassage at a speed sufficient said body for discharging well bore fluidsthrough to induct a sample of producible connate fluids said fluidpassage and in a reverse direction g from an earth formation incommunication with through said filtering means and into an earthforsaid fluid-admitting means into said fluid passage mation to cleansesaid filtering means of potentialand said expanded test chamber formomentarily ly-plugging material upon opening of said first reducing thepressure of a connate fluid sample to valve means. about atmosphericpressure. 22. The formation-testing apparatus of claim 21 fur- 26. Theformation-testing apparatus of claim25 further including: therincluding:

pressure-measuring means adapted for providing an a sample chamber onsaid body, and fourth valve indication of the pressure conditions insaid fluid means selectively operable for coupling said sampassage. plechamber to said fluid passage to receive con- 23. The formation-testin gapparatus of claim 21 furna'te fluids entering said fluid-samplingmember. ther including:

UNITED STATES PATENT OFFICE CE.TEFECATE 0F CORRECTIGN PATENT NO.3,813,936 DATED 3 June 4, 'NVENTOWS) 1 Harold J. Urbanosky and Frank R.Whitten It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

3 Column 2, line 12, "13" should read a Column 2, line 31, delete "A andB". Column 3, line 28, "borehole" should read The Column 4, line 19,"tublar" should read tubular Column 4, line 36,"2" should read 52 Column4, line 52, "menas" should read means Q Column 8, line 24,"pressure-actuated" should read imposed Column 8, line 27, delete "23".Column 8, line 44, following "line" insert 96 Column 9, line 42,"systems" should read system Column 10, line 66, "wil" should read willColumn 10 line 68, "197" should read 97 9 Column 12, line 15 "wall"should read well Column 14, line 63, "position" should read portionColumn 16, line 42, "11'' should read in Column 17, line 31,"saidenclosed" should read said enclosed Column 18, line 3, "sand"should read and Column 19, line 14, "chamber" should read member Column20, lines 57-58, delete "coupled medium".

Column 20, lines 58-59, delete "said and". Column 21, lines 42-43,delete "said and". Column 22, lines 24-24, delete "said and". Column 22,line 35, "agaln" should read again Sugncd and Scaled this rst a 0 mm 1 Dy f June1976 o Arrest:

RUTH C. MACON C. MARSHALL DANN Q Commissioner nfParerm and Trademarks

1. A method for testing earth formations traversed by a well bore andcomprising the steps of: engaging fluid-admitting means coupled by afiltering medium to a fluid passage against a wall surface of said wellbore adjacent to an earth formation believed to contain producibleconnate fluids for isolating said wall surface from fluids in said wellbore and placing said fluid-admitting means in position for receivingconnate fluids from said earth formation; discharging said well borefluids from said fluid passage in a reverse direction through saidfiltering medium and into said fluid-admitting means and said earthformation for cleansing said filtering medium; and, thereafter,communicating said fluid passage with an enclosed chamber initially at areduced pressure for drawing producible connate fluids from said earthformation and in the opposite direction through said filtering mediumand into said fluid passage to obtain a filtered sample of said connatefluids in said enclosed chamber.
 2. The method of claim 1 furtherincluding the additional step of: measuring the pressure in saidenclosedchamber and said fluid passage for obtaining at least one pressuremeasurement indicative of at least one characteristic of said earthformation.
 3. The method of claim 1 further including the additionalsteps of: monitoring at least one characteristic of said filtered sampledrawn into said fluid passage for obtaining a series of measurementsrepresentative of the production characteristics of said earthformatioN; and, thereafter, discontinuing further communication betweensaid fluid passage and said enclosed chamber for trapping said filteredsample therein.
 4. The method of claim 1 further including theadditional steps of: monitoring at least one characteristic of saidfiltered sample drawn into said fluid passage for obtaining a series ofmeasurements representative of the production characteristics of saidearth formation; and, thereafter, expelling said filtered sample fromsaid enclosed chamber.
 5. A method for testing earth formationstraversed by a well bore and comprising the steps of: urgingfluid-admitting means including a normally-closed fluid-sampling membercoupled by a filtering medium to a fluid passage into sealing engagementwith a wall surface of said well bore adjacent to an earth formationbelieved to contain producible connate fluids for isolating said wallsurface from fluids in said well bore and placing said fluid-samplingmember in position for subsequently communicating with said earthformation; opening said fluid-sampling member and admitting said wellbore fluids into said fluid passage for passing said well bore fluidsthrough said filtering medium and said fluid-sampling member into saidearth formation to cleanse said filtering medium sand saidfluid-sampling member of potentially-plugging materials; closingcommunication between said well bore fluids and said fluid passage; and,thereafter, coupling an enclosed reduced-pressure chamber to said fluidpassage for drawing producible connate fluids from said earth formationthrough said fluid-sampling member and said filtering medium and intosaid fluid passage to obtain a filtered sample of said connate fluids insaid enclosed chamber.
 6. The method of claim 5 further including theadditional step of: uncoupling said enclosed chamber from said fluidpassage for collecting said filtered sample.
 7. The method of claim 5further including the additional steps of: monitoring the pressure insaid fluid passage for obtaining a series of pressure measurementsrepresentative of the production characteristics of said earthformation; and uncoupling said enclosed chamber from said fluid passagefor collecting said filtered sample in said enclosed chamber.
 8. Themethod of claim 5 further including the additional steps of: monitoringthe pressure in said fluid passage for obtaining a series of pressuremeasurements representative of the production characteristics of saidearth formation; expelling said filtered sample from said enclosedchamber and uncoupling said enclosed chamber from said fluid passage;reclosing said fluid-sampling member; reducing the pressure in saidenclosed chamber; removing said fluid-admitting means from said wallsurface and urging said fluid-admitting means into sealing engagementwith another wall surface of said well bore adjacent to another earthformation believed to contain producible connate fluids for isolatingsaid other wall surface from said well bore fluids and placing saidfluid-sampling member in position for subsequently communicating withsaid other earth formation; re-opening said fluid-sampling member andre-admitting said well bore fluids into said fluid passage for passingsaid well bore fluids through said filtering medium and saidfluid-sampling member into said other earth formation to recleanse saidfiltering medium and said fluid-sampling member of potentially-pluggingmaterials; reclosing communication between said well bore fluids andsaid fluid passage; recoupling said enclosed chamber to said fluidpassage for drawing producible connate fluids from said other earthformation through said fluid-sampling member and said filtering mediumand into said fluid passage to obtain a filtered sample of said connatefluids from said other earth formation in said enclosed chamber; andremonitoring the pressure in said fluid passage for obtaining a secOndseries of pressure measurements representative of the productioncharacteristics of said other earth formation.
 9. The method of claim 5further including the additional steps of: monitoring the pressure insaid fluid passage for obtaining a series of pressure measurementsrepresentative of the production characteristics of said earthformation; coupling a sample receiver at a reduced pressure to saidfluid passage for collecting filtered connate fluids from said earthformation in said sample receiver; closing said sample receiver forentrapping connate fluids collected therein; expelling said filteredsample from said enclosed chamber and uncoupling said enclosed chamberfrom said fluid passage; reclosing said fluid-sampling chamber; removingsaid fluid-admitting means from said wall surface and urging saidfluid-admitting means into sealing engagement with another wall surfaceof said well bore adjacent to another earth formation believed tocontain producible connate fluids for isolating said other wall surfacefrom said well bore fluids and placing said fluid-sampling member inposition for subsequently communicating with said other earth formation;re-opening said fluid-sampling member and re-admitting said well borefluids into said fluid passage for passing said well bore fluids throughsaid filtering medium and said fluid-sampling member into said otherearth formation to recleanse said filtering medium and saidfluid-sampling member of potentially-plugging materials; reclosingcommunication between said well bore fluids and said fluid passage;recoupling said enclosed chamber to said fluid passage for drawingproducible connate fluids from said other earth formation through saidfluid-sampling member and said filtering medium and into said fluidpassage to obtain a filtered sample of said connate fluids from saidother earth formation in said enclosed chamber; and remonitoring thepressure in said fluid passage for obtaining a second series of pressuremeasurements representative of the production characteristics of saidother earth formation.
 10. The method of claim 9 further including theadditional step of: following the remonitoring step, coupling a secondsample receiver at a reduced pressure to said fluid passage forcollecting filtered connate fluids from said other earth formation insaid second sample receiver; and closing said second sample receiver forentrapping connate fluids collected therein.
 11. The method of claim 5further including the additional steps of: monitoring the pressure insaid fluid passage for obtaining a series of pressure measurementsrepresentative of the production characteristics of said earthformation; expelling said filtered sample from said enclosed chamber anduncoupling said enclosed chamber from said fluid passage; reclosing saidfluid-sampling member; reducing the pressure in said enclosed chamber;removing said fluid-admitting means from said wall surface and urgingsaid fluid-admitting means into sealing engagement with another wallsurface of said well bore adjacent to another earth formation believedto contain producible connate fluids for isolating said other wallsurface from said well bore fluids and placing said fluid-samplingmember in position for subsequently communicating with said other earthformation; re-opening said fluid-sampling member and re-admitting saidwell bore fluids into said fluid passage for passing said well borefluids through said filtering medium and said fluid-sampling member intosaid other earth formation to recleanse said filtering medium and saidfluid-sampling member of potentially-plugging materials; reclosingcommunication between said well bore fluids and said fluid passage;recoupling said enclosed chamber to said fluid passage for drawingproducible connate fluids from said other earth formation through saidfluid-sampling member and said filtering medium and into said fluidpassage to obtain a filtered sample of said connate fluids from saidother earth formation in said enclosed chamber; remonitoring thepressure in said fluid passage for obtaining a second series of pressuremeasurements representative of the production characteristics of saidother earth formation; coupling a sample receiver at a reduced pressureto said fluid passage for collecting filtered connate fluids from saidother earth formation in said sample receiver; and closing said samplereceiver for entrapping connate fluids collected therein.
 12. A methodfor testing earth formations traversed by a well bore and comprising thesteps of: urging fluid-admitting means including a fluid passage coupledby a filtering medium to a fluid-sampling member having anormally-closed forward end and a rearward portion to the rear of saidfiltering medium into sealing engagement with a wall surface of saidwell bore adjacent to an earth formation believed to contain producibleconnate fluids for isolating said wall surface from fluids in said wellbore and placing said closed end of said fluid-sampling member intoposition for subsequently receiving connate fluids from said earthformation; opening said normally-closed forward end of saidfluid-sampling member and admitting said well bore fluids into saidfluid passage for passing said well bore fluids through said filteringmedium and said fluid-sampling member into said earth formation tocleanse said filtering medium and said fluid-sampling member ofpotentially-plugging materials; closing communication between said wellbore fluids and said fluid passage; expanding the volume of an enclosedtest chamber coupled to said fluid passage downstream of said filteringmedium for reducing the pressure in said fluid passage and said testchamber to about atmospheric pressure; after said test chamber isexpanded, coupling said test chamber to said fluid passage at a speedsufficient to quickly induct a filtered sample of producible connatefluids from said earth formation into said expanded test chamber formomentarily reducing the pressure of said connate fluid sample to aboutatmospheric pressure and displacing loose plugging materials from saidwall surface into said rearward portion of said fluid-sampling member tothe rear of said filtering medium; and monitoring the pressure in saidexpanded test chamber for obtaining a series of pressure measurementsindicative of the production capabilities of said earth formation. 13.The method of claim 12 further including the additional step of:recording said pressure measurements for obtaining a recordrepresentative of the pressure characteristics of said earth formationas connate fluids are produced therefrom.
 14. The method of claim 12further including the additional step of: after the pressure-monitoringstep, coupling an enclosed sample chamber to said fluid passagedownstream of said filtering medium for collecting another filteredsample of connate fluids from said earth formation.
 15. The method ofclaim 12 further including the additional steps of: after thepressure-monitoring step, reducing the volume of said test chamber forexpelling said sample of connate fluids into said well bore; uncouplingsaid test chamber from said fluid passage; reclosing saidnormally-closed forward end of said fluid-sampling member; re-openingsaid normally-closed forward end of said fluid-sampling member andre-admitting said well bore fluids into said fluid passage for againpassing said well bore fluids through said filtering medium and saidfluid-sampling member into said earth formation to recleanse saidfiltering medium and said fluid-sampling member for potentially-pluggingmaterials; reclosing communication between said well bore fluids andsaid fluid passage; re-expanding the volume of said test chamber foragain reducing the pressure in said fluid passage and said test chamberto about atmospHeric pressure; after said test chamber is re-expanded,re-coupling said re-expanded test chamber to said fluid passage at aspeed sufficient to quickly induct a second filtered sample ofproducible connate fluids into said re-expanded test chamber formomentarily reducing the pressure of said second sample to aboutatmospheric pressure and displacing additional loose plugging materialsfrom said wall surface into said rearward portion of said fluid-samplingmember to the rear of said filtering medium; and re-monitoring thepressure in said re-expanded test chamber for obtaining a second seriesof pressure measurements indicative of the production capabilities ofsaid earth formation.
 16. The method of claim 15 further including theadditional step of: after obtaining said pressure measurements, couplingan enclosed sample chamber to said fluid passage downstream of saidfiltering medium for collecting another filtered sample of connatefluids from said earth formation.
 17. The method of claim 15 furtherincluding the additional steps of: after obtaining said pressuremeasurements, reducing the volume of said test chamber again forexpelling said second sample into said well bore; reclosing saidnormally-closed forward end of said fluid-sampling member; anddisengaging said fluid-admitting means from said wall surface.
 18. Themethod of claim 12 further including the additional steps of: after thepressure-monitoring step, coupling an enclosed sample chamber to saidfluid passage downstream of said filtering medium for collecting anotherfiltered sample of connate fluids from said earth formation; reducingthe volume of said test chamber for expelling said sample of connatefluids into said well bore; uncoupling said test chamber from said fluidpassage; reclosing said normally-closed forward end of saidfluid-sampling member; re-expanding the volume of said test chamber foragain reducing the pressure in said fluid passage and said test chamberto about atmospheric pressure; disengaging said fluid-admitting meansfrom said wall surface and urging said fluid-admitting means intosealing engagement with another wall surface of said well bore adjacentto another earth formation believed to contain producible connate fluidsfor isolating said other wall surface from said well bore fluids;re-opening said normally-closed forward end of said fluid-samplingmember and re-admitting said well bore fluids into said fluid passagefor aga1n passing said well bore fluids through said filtering mediumand said fluid-sampling member into said other earth formation torecleanse said filtering medium and said fluid-sampling member ofpotentially-plugging materials; reclosing communication between saidwell bore fluids and said fluid passage; re-coupling said re-expandedtest chamber to said fluid passage at a speed sufficient to quicklyinduct a second filtered sample of producible connate fluids into saidre-expanded test chamber for momentarily reducing the pressure of saidsecond sample to about atmospheric pressure and displacing looseplugging materials from said other wall surface into said rearwardportion of said fluid-sampling member to the rear of said filteringmedium; and re-monitoring the pressure in said re-expanded test chamberfor obtaining a second series of pressure measurements indicative of theproduction capabilities of said other earth formation.
 19. The method ofclaim 18 further including the additional steps of: after obtaining saidsecond series of pressure measurements, coupling an enclosed samplechamber to said fluid passage downstream for collecting another sampleof connate fluids from said other earth formation.
 20. The method ofclaim 18 further including the additional steps of: after obtaining saidsecond series of pressure measurements, reducing the volume of said testchamber again for expelling said second sample into said well bore;uncoUpling said test chamber from said fluid passage; re-closing saidnormally-closed end of said fluid-sampling member; and disengaging saidfluid-admitting means from said other wall surface. 21.Formation-testing apparatus adapted for suspension in a well boretraversing earth formations and comprising: a body having a fluidpassage adapted to receive connate fluids; fluid-admitting means on saidbody including a fluid-sampling member having a forward end adapted tobe selectively engaged with a well bore wall for isolating a portionthereof from well bore fluids, first valve means normally closing saidforward end of said fluid-sampling member, and filtering means couplingsaid fluid passage to said fluid-sampling member to the rear of saidfirst valve means; means on said body and selectively operable forpositioning said fluid-admitting means against a well bore wall to placesaid fluid-sampling member in communication with earth formations beyondsaid well bore wall; and control means including second valve meansselectively coupling said fluid passage to the exterior of said body fordischarging well bore fluids through said fluid passage and in a reversedirection through said filtering means and into an earth formation tocleanse said filtering means of potentially-plugging material uponopening of said first valve means.
 22. The formation-testing apparatusof claim 21 further including: pressure-measuring means adapted forproviding an indication of the pressure conditions in said fluidpassage.
 23. The formation-testing apparatus of claim 21 furtherincluding: sample-collecting means on said body including a samplechamber, and means selectively operable for coupling said sample chamberto said fluid passage to receive connate fluids entering saidfluid-admitting means.
 24. The formation-testing apparatus of claim 23further including: pressure-measuring means adapted for providing anindication of the pressure conditions in said fluid passage.
 25. Theformation-testing apparatus of claim 21 further including:pressure-reducing means on said body including an enclosed test chamber,and means selectively operable for varying the volume of said testchamber including piston means movable back and forth between a firstposition reducing the volume of said test chamber and a second positionsufficiently expanding the volume of said test chamber to reduce thepressure in said test chamber to about atmospheric pressure;pressure-measuring means adapted for providing indicationsrepresentative of the pressure conditions in said test chamber; andcontrol means selectively operable after movement of said piston meansto said second position and including third valve means for couplingsaid test chamber to said fluid passage at a speed sufficient to inducta sample of producible connate fluids from an earth formation incommunication with said fluid-admitting means into said fluid passageand said expanded test chamber for momentarily reducing the pressure ofa connate fluid sample to about atmospheric pressure.
 26. Theformation-testing apparatus of claim 25 further including: a samplechamber on said body, and fourth valve means selectively operable forcoupling said sample chamber to said fluid passage to receive connatefluids entering said fluid-sampling member.